1. Field of the Invention
The present invention relates to a lens unit having an aperture inside, a camera system, and a control method for an aperture.
2. Description of the Related Art
In order to control exposure so as to achieve correct exposure, an aperture unit is provided within a lens unit. The aperture unit requires high speed drive at the time of still picture shooting, while requiring low speed drive at the time of movie shooting. In order to satisfy these two drive conditions, an imaging apparatus that has a motor for low speed drive and a motor for high speed drive provided in an aperture unit to cover situations from low speed to high speed, and ensures drive time and performance at the time of low speed, is proposed in Japanese patent laid-open No. 2013-127527 (hereafter referred to as patent publication 1).
By providing two motors, as with the imaging apparatus disclosed in patent publication 1, it is possible to lower drive noise at the time of still picture shooting and at the time of movie shooting, and to ensure drive stability. However, at the time of aperture drive, in a case where linearity is not ensured in change of light amount passing through the aperture as a result of drive control of an aperture drive motor, exposure will change unnaturally.
Change in light amount of subject light flux that passes through the aperture is dependent upon cam shape of an aperture unit, and change in light amount becomes non-constant due to nonlinearity of change in aperture opening area. Generally, in order to miniaturize a lens unit, the shape of a cam may be set so that change in aperture opening area becomes nonlinear. In this way, since exposure changes unnaturally because of aperture unit cam shape, it leads to unappealing images at the time of live view display and at the time of movie playback.